Public Switched Telephone Networks (PSTN) are of major importance in the data transmission field since they can be used in order to communicate data from a first local data terminating equipment (DTE) to a second, remote, DTE. The attachment of a DTE to a telephone network requires a device known as a DCE or modem which particularly includes a coupler circuit for providing the adaptation of the electrical signals to the characteristics of the switched telephone network to which the DCE is likely to be connected.
With the development of sophisticated systems allowing the powerfull processing and use of vocal messages in data processing systems, a need has appeared in a device that allows the transmission of voice from a local telephone set to a data processing system via a DCE. However, coupler circuits which are known in the art does not allow that possibility since the local telephone set operates only when it is connected to the PSTN and consequently can not be used from transmitting voice messages through the DCE into the local DTE.